(Girl) Guides

Post by **rupert** » Sun Apr 04, 2004 8:45 pm

Hi All, the valve guides on my 12G295 head are a bit vague, I've heard that new ones can be fitted at home. Is it as simple as drifting out the old ones and drifting in the new ones or is there more to it?

thanks

Rupert

Post by **les** » Sun Apr 04, 2004 9:29 pm

Basically the answer is yes, although before fitting the new ones it might be considered good practice to heat the head and cool the guides, but there is a measurement that must be maintained which is from the top of the guide to the head deck, which I think is in the manual, however you can check this dimension before you remove the old ones. When fitting the new guides use a spigot that locates IN the guide as well as on top, this avoids burring the inside diameter when knocking in. If you do make a burr carefully ream the guide top to remove, otherwise the valve stem will be tight at this point.

Post by **brixtonmorris** » Sun Apr 04, 2004 9:41 pm

the fit is called an 'interference fit' they overlap by a few thou, difficult to deal with without a press and squareness type tools. you dont want them to come lose at full speed.

Post by **Alec** » Mon Apr 05, 2004 9:13 am

Hello Rupert,
Guides can be driven out and replaced, using a stepped guide. You can get away with using a snug fitting bolt but be prepared to dress the top of the guide. However, then the valve seats want re-cutting when the guides are replaced.

Alec

Post by **newagetraveller** » Mon Apr 05, 2004 3:54 pm

I have done this myself but:
(a) I got a friend with a lathe to make me the tool that is described in the workshop manual and
(b) you have to be very careful in order to knock the new guide in by exactly the right amount.

Post by **les** » Mon Apr 05, 2004 8:18 pm

Talking about interference fit, did you know that a 10mm bar wont fit in a 10mm hole!

Post by **Alec** » Tue Apr 06, 2004 7:16 am

Hello Les,
only if the bar is square and the hole is round, there again, some fitters and their hammers I have known !!!.

Alec

Post by **Kevin** » Tue Apr 06, 2004 11:24 am

Talking about interference fit, did you know that a 10mm bar wont fit in a 10mm hole!

Good one Les, in theory of course they would fit but in reality the friction stops them going together without assistance from a third party device.

Alec here is a good one for you unless you already know the answer. Do you know how to make a single piece of metal fit into a 1" square hole, a 1" triangular hole (right angled triangle) and a 1" hole with no gaps in any of the holes ?

Post by **paulg** » Tue Apr 06, 2004 11:51 am

ok, takes deep breath and orders flak jacket in preparation for expected incoming!
I have fitted valve guides with a brass drift only, establishing depth by eye against a marked piece of dowel. Care and gentleness is needed, with perhaps a bit of courageous force to finish with!.
It didn't take long and they are ok. The worst part is drifting them out - they can break up.
One original valve guide was free in the head, so there was a double action with the valve moving in the guide and the guide in the head!
The new one being a loose fit, I burred the hole for the valve guide in the head (carefully) with a steel punch before drifting in the guide with loctite smeared in the hole - seems to have worked!
I ground the valves in with paste (not recut by machine) and the wear pattern showed a good seat.
Compression was 155/160.
So perhaps not absolutely correct practice, but a cheap and effective repair that has lasted very well!

Post by **Kevin** » Tue Apr 06, 2004 2:02 pm

I have fitted valve guides with a brass drift only

Nothing wrong with that as long as it finished in the correct position.

The new one being a loose fit, I burred the hole for the valve guide in the head (carefully) with a steel punch before drifting in the guide with loctite smeared in the hole - seems to have worked!

Not come across that problem before and only time will prove the effectiveness of the repair. I assume the guides only come in one external size and the only other solution would be a sleeve inserted in the head and then reamed back to original size

Post by **paulg** » Tue Apr 06, 2004 2:59 pm

Sleeve would have been microns thick unless hole was drilled etc! Anyway, this wasn't really an option - the car was needed!

Post by **les** » Tue Apr 06, 2004 7:53 pm

I've seen bearing housings mutilated by centre punch, to 'cure' a loose fit.
Remember, don't have nightmares!